Capacitor-discharge electronic ignition system

ABSTRACT

A battery-powered capacitor discharge type of ignition system for a piston engine in which the storage capacitor is charged through a DC-to-DC power converter the output of which is fed to the storage capacitor through an inductance capacitance circuit. A silicon-controlled rectifier means in series with the storage capacitor and a primary ignition coil in a discharge circuit having a diode and capacitor in parallel therein, is triggered by a pulse generated by a circuit powered from the battery and operated in synchronism with the breaker points.

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Priman Examiner-Laurence M. Goodridge Attorney-Wham and McManigal [54] CAPACITOR-DISCHARGE ELECTRONIC IGNITION SYSTEM 2 Claims, 2 Drawing Figs.

ABSTRACT: A battery-powered capacitor discharge type of ignition system for a piston engine in which the storage capaci- 315/209 tor is charged through a DC-to-DC power converter the out- F02p 3/06 [5]] Int. put of which is fed to the Storage capacitor through an i [50] Field of 123/148 E; ductance capacitance circuit A smcomcomroued ifi means in series with the storage capacitor and a primary ignition coil in a discharge circuit having a diode and capacitor in parallel therein, is triggered by a pulse generated by a circuit powered from the battery and operated in synchronism with 123/148 E the breaker points.

[56] Referenc'es Cited UNITED STATES PATENTS 3,127,540 3/1964 Collins CAPACITOR-DISCHARGE ELECTRONIC IGNITION SYSTEM BACKGROUND OF INVENTION This invention relates generally to ignition systems for internal combustion engines, and particularly relates to a solid state electronic ignition circuit designed especially for automotive engines.

Any ignition system for an automotive engine must be capable of delivering a high voltage pulse capable of firing the spark plugs of the engine regardless of the engine speed. The engine speed usually varies over a very wide range from idling to the top speed. By way of example, the idle speed may be a few r.p.m. while the top engine speed may be as high as 10,000 rpm. or greater. This, in turn, means that the ignition system, whether electronic or not, must be capable of furnishing the high voltage pulses to the spark plugs at speeds up to 700 cycles per second or more for an eight-cylinder, four-cycle engine.

CROSS-REFERENCE TO RELATED APPLICATION In my copending application entitled Capacitor Discharge Electronic Ignition System and a Method for Adjusting the Circuit, Ser. No. 577,51l, filed Sept. 6, 1966, now US. Pat. No. 3,448,732 I disclose a capacitor-dischage electronic ignition system in which there is a storage capacitor which is fed through an inductance capacitance circuit. In this system there is a switch means in series with the storage capacitor and a primary of the ignition coil which forms a discharge circuit which is triggered by a pulse generated by a circuit powered from the battery and operated in synchronism with the breaker points of the distributor.

My present invention is a capacitor discharge electronic ignition system intended or the same use as my prior invention, but embodying certain hereinafter described and illustrated improvements which provide for superior and different results.

SUMMARY OF INVENTION My invention comprises a device as heretofore referred to, including means to generate successive pulses of high voltage to charge a large capacitor, and includes unique means to trigger an SCR means to trigger the large capacitor and cause a reverse charge on it to thus provide a high voltage pulse through a primary coil to induce a very high negative voltage through a secondary coil in a direction to fire a spark plug.

It is an object of my invention to provide a system of the character referred to wherein there are two power supply means connected in dual parallel fashion in order to double the frequency rate of charging the power supply without increasing the power level in order to fully charge a capacitor in a minimum period of time without incurring excessive voltages.

It is another object of my invention to prevent or reduce to a minimum the negative surge in the trigger circuit of the SCR means, to reduce and eliminate destructive effect thereof on the SCR means.

It is an object of my invention to provide an arrangement wherein a diode is connected between the trigger circuit and ground potential, which functions to protect the gate or gates of the SCR means from receiving excessive negative voltages during a tiring cycle.

It is a further object of my invention to provide in a system of the character referred to means to absorb stray voltages, spike noise voltages, and unwanted voltage pulses when the distributor points close.

It is a further and more specific object of my invention to provide a capacitor which is connected to ground potential and to the triggering circuit of the gate or gates which functions to absorb unwanted voltage pulse as distinguished from the voltage pulse produced when breaker points of the distributor open to fire the SCR means into conduction.

It is another of the objects of my invention to provide a system wherein two SCRs are connected in dual parallel fashion to diminish the resistance by one-half in SCR conduction thereby doubling the current How in SCR switching thus providing for a faster transfer of electrical energy stored in the capacitor into the primary winding of the ignition coil resulting in a steeper slope to provide a hotter spark at the spark plug.

Other objects and advantages of the invention will be brought out during the course of the following detailed description of my invention.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a circuit diagram of the electronic ignition system of the invention shown in connection with a portion of the standard ignition system of an automobile, the drawing indicating schematically the points to be connected by a cable and optionally by a switch. This view illustrates the dual parallel power supply of my invention and also the improved triggering means for discharging the storage capacitor; and

FIG. 2 is a fragmentary schematic circuit diagram showing a second form of capacitor-dischaging means.

DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION Referring now to the drawing, and particularly FIG. 1, there is illustrated an electronic circuit embodying the present invention and cooperating with a portion of the conventional ignition system of an automotive engine. The parts of the circuit showing components of the conventional automobile ignition system are shown in dotted boxes. Thus, dotted lines 10 enclose the car battery, the ignition switch, the starter relay and indicate the starter motor. Dotted lines I] enclose the distributor with one set of points shown schematically, while dotted lines 12 enclose one of the spark plugs and the ignition coil.

Thus, within box 10 there is shown a battery 15 conventionally provided in any car which may have its negative terminal grounded as shown. This may, for example, be a l2-volt battery as has become conventional for late model automobiles. The positive terminal of the battery 15 is connected to the ignition switch 16 which in turn is connected through a ballast resistor 17 to the output line 18. The ignition switch may have an additional contact 20 which is operated for starting the engine to connect the relay 21 to the positive pole of the battery 15. The other end of the relay coil may be grounded as shown. Thus, energization of the starter relay 21 may close a switch 22, which connects the lead 18 carrying the positive voltage supply to the starter motor indicated by the line 23, thereby to start the engine. When the solenoid of the relay 21 is energized to start the starter motor, the ballast resistor 17, which is a necessary feature for conventional systems for cold weather starting, is bypassed so that the full battery voltage is supplied to the ignition coil. Switch 19, a set of contacts on the multiple switch that connects the cable to the automobile's electrical system, is provided in the unit to bypass ballast resistor 17, that is, ballast resistor 17 is paralleled, when the ignition key is returned to ignition ON" after the engine is started. The bypass or parallel switch 19 is necessary in automobile ignition systems where the current drain is 5 amps or less, thus providing full battery supply to the unit during all speeds and driving conditions. Since switch 19 is an integral part of the electronic ignition unit, it is automatically disconnected as a bypass circuit and restores ballast resistor 17 into the automobiles electrical system when the master or multiple switch that connects the cable is switched to the car's original conventional system.

Within the dotted box 11 there is shown schematically at 25 the distributor which may include a cam 26 driven by the engine crankshaft and a pair of distributor points 27. An ignition capacitor 28 may be connected across the points 27 to minimize arcing.

The dotted box 12 encloses a primary winding 30 and a secondary winding 31 forming together the ignition autotransformer. The secondary winding 31 is connected to the spark plug 32. One of the terminals of the spark plug 32 such as its base may be grounded as shown through the lead 33.

The electronic circuit of the present invention includes a pair of voltage converters 35 and 35A for converting the DC (direct current) battery voltage into a higher AC (alternating current) voltage which may subsequently be rectified by fullwave rectifier networks 36 and 36A. The two converters are identical, having corresponding parts. The parts of converter 35A will be given the same number as the similar parts of converter 35 with the suffix A" added, except that capacitor 48 and capacitor 58 are.not duplicated. These capacitors serve a common function to both converters The voltage converters 35 and 35A are connected to the output lead 18, then through the closed bypass switch 19 which bypasses ballast resistor 17 and ignition switch 16 to the positive terminal of battery 15.

I will now describe the converter 35, it being understood that this description also covers the converter 35A which is in parallel thereto.

The lead 18 connects through a lead 37 to the center point of the primary winding 38 of a converter transformer 40 having a secondary winding 41 and a control or feedback winding 42. The transformer 40 has a saturating core with a square hysteresis curve such as is available from a ferroxcube core. A pair of transistors 43 and 44 have their collectors connected to i the terminals of the primary winding 38 while their emitters are tied together to ground through lead 50 and to respective anodes of a pair of diodes 45 and 46. The cathode of diode 45 is connected to one tenninal of feedback winding 42 and to the base of transistor 43, while the other terminal of winding 42 is connected through an adjustable resistor 47 back to the cathode of the diode 46 and the base of the transistor 44.

A capacitor 48 may be connected between the center tap of primary winding 38 and the two emitters of the two transistors 43 and 44. Furthermore, a resistor 51 is connected between the center tap of the primary winding 38 and the base of transistor 44.

The capacitor 48 connected between the midpoint of the primary winding 38 and ground serves the purpose to suppress radio frequency currents which may be generated in the electronic circuit of the invention and for preventing such radiofrequency currents from appearing in the electrical system of the car. It serves the additional purpose to smooth out the ripples or voltage variations of the battery of the car which powers the transistors 43 and 44.

This voltage converter 35 operates in a conventional manner. The two transistors 43 and 44 are alternatively permitted to conduct and, hence, to cause a current flow through either one-half or the other of the primary transformer 38. The two transistors are controlled through their bases in accordance with the voltages developed at the terminals of the feedback winding 42, which alternatively permits each transistor to conduct in a manner well known in the art.

As a result a relatively high alternating voltage is developed across the secondary winding 41. This alternating voltage is rectified by the full-wave rectifier networks 36. This includes a rectifier bridge 55 having two terminals 56 and 57 connected directly across the secondary winding 41. A filter and smoothing capacitor 58 is connected across the other two terminals 60 and 61 which are the output terminals of the fullwave rectifier networks 36 and 36A. The output terminals 60A and 61A are connected by lines 6013 and 618 to the terminals 60 and 61. As indicated, a positive voltage appears at the point 61 and a negative voltage at the point 60. A diode rectifier 62 may have its anode connected to the point 61 in series with a DC voltmeter 63 having its other terminal connected to the point 60. The voltmeter 63 has a high internal resistance (300,000 ohm-300-volt full-scale meter times 1,000 ohms equals 300,000 ohms). Thus, the 300,000 ohms serve the dual purpose of operating the DC voltmeter and regulating the power supply between the positive terminal 61 and the negative terminal 60 which is necessary to suppress voltage spikes at the full B-plus power supply level that may be damaging to the SCR and permits to observe continuously the actual DC voltage across the full-wave rectifier, which may be nominally of the order of 250 volts DC. The double power supply in parallel provides double the frequency of power pulses without increasing the power level.

Controlled rectifiers 65 and 65A, such as a silicon controlled rectifier, have their anodes connected to the point 61 carrying the positive output voltage of the dual high voltage source. The cathodes are connected to grounded leads 66 and 66A respectively. Triggering lines 67 and 67A are connected to lead 68, thus placing them in parallel. Diode 106 is connected between ground 66 and lead 68, and capacitor 107 is connected between the ground and lead 68, thus these elements 106 and 107 are in parallel with lead 68, diode 70 and variable inductor 71 to the negative terminal 60 of the high voltage source provided by the rectifier network 36 and 36A.

The positive output terminal 61 of the bridge rectifiers may be grounded through a diode 73 having its cathode connected to point 61 and its anode grounded as shown.

A charge storage capacitor 76 which is periodically discharged by the controlled rectifiers 65 and 65A is connected in series between the positive terminal of the primary winding 30 of the ignition coil and the positive terminal 61.

A diode 77 has its anode connected to ground while its cathode is connected directly to one terminal of the variable inductor 71. The junction of diode 80 and resistor 81, connected in parallel is connected through lead 68 to diode 70 having its cathode connected to the cathode of the diode 77. Diode 80 and resistor 81 connected in parallel are, in turn, connected to a control or signal generating capacitor 82. The capacitor 82, in turn, is connected to a lead 83 connected to the distributor25. A resistor 84 may be connected between the lead 83 and the lead 37 which is returned to the center of the primary winding 38 and to the positive terminal of the battery via closed bypass switch 19 and closed ignition key 16.

The operation of the circuit illustrated in the drawing will now be explained.

When the ignition switch 16 is closed, the voltage of battery 15 is applied to the voltage converters 35 and 35A through ballast resistor 17, parallel or bypass switch 19, and lead 18. Also, as is conventional, the ignition switch may be further moved to connect contact 20 to the positive pole of battery 15, thereby to energize the starter relay 21 and the starter motor which is connected to the lead 23. When the starter motor is energized to turn the engine, ballast resistor 17 is automatically bypassed by the starter relay in the conventional operation, but ballast resistor 17 is bypasses or paralleled by switch 19 at all times when the capcitor-discharge electronic ignition system is in operation. When the original ignition system is used, ballast resistor 17 is restored to its original function in the circuit. In that case the ignition system of the invention receives the entire voltage of the battery 15. This promotes easier startingdue to the heavy current drain on the battery 15 to drive the starter motor connected to the lead 23. Such an arrangement is particularly useful where the current drain through the ignition coil is 5 amperes or less.

The voltage converters 35 and 35A now operate as follows: the transistors 43 and 43A and 44 and 44A are alternately energized to permit the flow of current from the center taps of the primary winding 38 and 38A throughalternate portions thereof. The conduction of the transistors 43 and 43A and 44 and 44A are controlled by their bases through the feedback windings 42 and 42A. Every time the base of one of the transistors becomes positive with respect to its emitter, the transistor conducts. The resistors 51 and 51A serve the purpose to control starting of the voltage converter. In other words, the voltage drop across the resistors 51 and 51A determines which of the transistors begins to conduct initially.

The resistors 47 and 47A which are adjustable, are connected in series with the feedback windings 42 and 42A. They may either be adjusted or else replaced by resistors of different resistence or by providing several resistors in parallel to apply the desired resistance. This permits to obtain maximum range. It also minimizes the occurrence of high current peaks which may otherwise occur at the extreme portions of the operating cycle as the current through each transistor approaches a maximum. 1

As stated before, the transformers 40 and 40A-have cores I which saturate and have a substantially square'wave hysteresis Y I curve. This provides a better inversion action of the circuit and gives a smoother output'voltagerThe two diodes'45 andi 46 and 45A and 46A preventcurrent flow in the conventional direction from the base to the emitter of each'transistor. In

other words, they prevent the bases-from becoming negative because the emitters are grounded.

Tl-le voltage converters 35 and 35A are designed to each have an operating frequency of (kilocycles per second). n v e e The output voltages of the voltageconverters aretra'nsconnected the full-wave rectitiers 36"and 36A. The" positive output voltage is obtained at the terminals 61 and 61A'vvhile a negative voltage is developed at the terminals 60 and 60A.

The output voltages are stored across th'e electrolytic capacitor 58 which filters out alternating current ripples and stores the electric charge to provide a smooth direct current supply between the terminals 60 and 61, the terminals 60A aiid 61A being connnected thereto by the lines 60Band 61B.

Optionally, there may be connected a voltmeter 63 'of high internal resistance (300,000 ohms) which serves the dual purpose of operating the DC voltmeter and srriooths out and regulates the power supply and diode 62 in series across the terminals 61 and 60 of the full-wave rectifier. This maybe effected by a cable connected across the connection -points indicated schematically at 86 and 87. The-cable makes it possible, for example, to display the voltmeter 63 at the dashboard of the car. The diode 62 acts asa blocking diode'and permits current to flow from terminal 61 to terminal 60throug'h'the voltmeter 63. Thus, it permits only current flow in one direction through the voltmeter 63 and thus prevents current leakage to the anodes of the silicon-controlled.rectifiers '65 and 65A while they are conducting and in the overswing positron.

The output voltage pulses at the terminal 61 (which may amount to 250 volts DC) by virtue of the two power sources in parallel, are produced at double the rateof a single power source; and this is accomplished without increasing the volt age amplitude above a safe maximum voltage. These fvoltage pulses charge the charging capacitor 76'which, in turn, is connected to ground through the primary winding 30 of the ignition coil. The charging circuit across the charging capacitor 76 may be traced from ground-through diode 77, choke coil 71 back to terminal 60 which; in turn, is connected through the filter capacitor 58 to terminal 61.

Thus, it will be noted that a circuit is provided-including -IT should-also be noted that the control or signal generating "capacitg'ir 82}"is charged'by the battery 15. This circuit can raced frortithe positive pole of the battery through the igition switch 16, ballast resistor 17 and paralleled or bypass switch 19, leads 18, 37, and resistor to the capacitor '82.

The function of control capacitor 82 is toicontrol the conducti'on of controlled rectifiers 65 and 65A in accordance with the operation of'the distributor, that is, in accordance with the engine speed. Thus when the breaker points 27 of the distributor are closed, the capacitor 82 is discharged through ground through thebreaker points 27 which, in turn, are grounded.

Thecapacitor 28 across the breaker points, of course, serves the p urpose to suppress sparks. The capacitor 28 furthermore forms a resonant; circuit with the primary winding 30 when the points 27 of thedistributor are open. A lso,.resistor 8,4 is a dropping resistor and limits the current flow through the breaker-points when the breaker points are closed. As soon as, the breaker points open again, the capacitor 82 isv charged again with the positive battery voltage throughdropping resistor 84. This positive charging voltage formed up by the secondary windings 4 1 and 41A, to'which is 1 t w d a P sigma Puisewhichis conflucled to the'gates of the controlledrectifiers 65 and 65A through diode 80 and --resistor 81,-'and portion 68A of line 68, thus making these .SCRS conductive. This'pennits the charge storage capacitor 76 to discharge directly to ground through the anode-cathode path of the controlled rectifiers. T he discharge circuit across the charge'storage' capacitor 76 is completed from ground by the opening ofthe breaker points 27 of the distributor 25.

may be as high as 700 cycles per se cbnd, depending on the number of cylinders and, of course, on the highest number of revolutions of the engine.

The spark plug 32 is tired by -suddenly discharging the capacitor 76 which, in turn, causes a" voltage surge across the '70 primary winding 30 of the ignition coil and a correspondingly higher voltage surge across thes'tfondary igiiition amongst. This is effected by the contrciliedlrectifiers 65 and 65A which are controlled by the operation oftheidistributor 25, that is, by the opening of the breaker p'oints 27 thereof.

On the other ;hand, the resonant circuit referred to heieinabove and including choke 71, primary ignition coil 30 and capacitors 58 and 76 should be turned to have a resonant frequency sufficiently high so that the charge storage capacitor 76 may be discharged throughout the operating range of the engine to fire the spark plugs of the car.

When silicomcont rolled rectifiers 65 and 65A tend to go toward an extreme negative voltage overswing position, the diode 106 prevents the excessive negative voltage condition from occuring because it connects the'triggering lines 67 and 67A to ground 66. By this arrangement the anode of the diode 106, being connected to ground potential, and the cathode being connected to the triggering lines 67 and 67A, the triggering circuit is thus connected to ground potential and this bleeds off excessive negative voltage and prevents the negative voltage from becoming excessive. This arrangement is a valuable protection for either or both of the SCRs 65 and 65A. in this form of my invention the arrangement of the SCRs in. dual parallel fashion will diminish the resistance to one half in the SCR conduction and this will double the current flow in SCR switching, thus enabling a faster transfer of the electrical energy 'stored in 'the capacitor 76. This, in turn, provides for a faster 'reversal'of voltage in the coil 30 and this results in a steeper slope and the production of a hotterspark in the spark plug 32. f

When the breaker points of the distributor 25 are open, control capacitor 82 is being charged to the l2-volt battery potential. At theins't'ant the breaker points close, the control capacitor 82' is grounded therethrough. 0n the other hand, the potential previously existing across the capacitor 82 must now be dissipate) without triggering the controlled rectifiers 65 and 65A into conduction again. To this end there is provided a relatively longftime constant for capacitor 82 which includes vresistor 81.1t should be noted that the negative voltage now provided at the gates of the controlled rectifiers through the diode 106 also aids in preventing false triggering of the rectifi- The capacitor 107 acts as a ballast and tends to smooth out spurious voltage spikes and retains electrical energy for a sufficient amount of time for the triggering pulse to tire the SCRs into conduction. Also, after the firing of the SCRs the capacitor 107 acts to absorb stray voltage spikes due to noiseand also unwanted voltage pulses when the points 27 again close. The inclusion of the diode 106 and the capacitor 107 in parallel between ground and the triggering lines 67 and 67A is an important and unique feature of my invention.

The important improvements relating to the diode and capacitor in parallel and the dualpower supply comprise the patentable improvements of the present invention. For other details my copending application, Ser. No. 577,511, referred to heretofore, may be referred to. Also, in this copending application the values for the various component parts are given and such values or substantially the same values would apply to the present application.

In FIG. 2, I illustrate an alternative form of my invention. This figure is a fragmentary view of the right part of the diagram of FIG. 1. In this alternative form of my invention there is but a single SCR 65 having a cathode connected to the ground 66. Connected between the ground 66 and the triggering line 67 is the diode 106 and thecapacitor 107. The mode of operation of this form of my invention is the same as in the form previously described. There is, of course, but a single SCR and this form of my invention, therefore, does not include the feature of reducing the resistance to one-half in the SCR condition. This form, however, has proven to be highly satisfactory in use. Other than the small change in operation resulting from the absence of the SCR 65A and the triggering line 67A, the construction and operation are the same as in FIG. 1.

I claim:

1. An electronic ignition system comprising:

a. a relatively low voltage first direct current source;

b. power supply means coupled to said first direct current source for developing a relatively high voltage to provide a second direct current source which has a low voltage and a high'voltage side;

- c. an ignition coil having a primary winding;

d. a charge storage capacitor connected between'said high voltage side of said second direct current source and said primary winding;

e. a controllable discharge path for said charge storage capacitor including a controlled rectifier for substantially instantaneously discharging said capacitor and for creating a high voltage surge in said primary winding;

f. a distributor having a plurality of points;

g. means connecting said distributor points across said first direct current source;

h. circuit means connected between the control element of said controlled rectifier and said distributor points for rendering said controlled rectifier conductive when the points of said distributor open after having been closed, thereby to apply a low voltage pulse to the control element of said controlled rectifier and to discharge said storage capacitor; and

means including a capacitor connected continuously in series between said control element of said control rectifier and ground to reduce negative voltage surges in the circuit to said control element.

2. A combination as defined'in claim 1 wherein there are two power supply means connected in dual parallel fashion including two full-wave rectifiers having their outputs connected in parallel in order to double the frequency rate of charging said storage capacitor without any substantial increase in power level. 

1. An electronic ignition system comprising: a. a relatively low voltage first direct current source; b. power supply means coupled to said first direct current source for developing a relatively high voltage to provide a second direct current source which has a low voltage and a high voltage side; c. an ignition coil having a primary winding; d. a charge storage capacitor connected between said high voltage side of said second direct current source and said primary winding; e. a controllable discharge path for said charge storage capacitor including a controlled rectifier for substantially instantaneously discharging said capacitor and for creating a high voltage surge in said primary winding; f. a distributor having a plurality of points; g. means connecting said distributor points across said first direct current source; h. circuit means connected between the control element of said controlled rectifier and said distributor points for rendering said controlled rectifier conductive when the points of said distributor open after having been closed, thereby to apply a low voltage pulse to the control element of said controlled rectifier and to discharge said storage capacitor; and means including a capacitor connected continuously in series between said control element of said control rectifier and ground to reduce negative voltage surges in the circuit to said control element.
 2. A combination as defined in claim 1 wherein there are two power supply means connected in dual parallel fashion including two full-wave rectifiers having their outputs connected in parallel in order to double the frequency rate of charging said storage capacitor without any substantial increase in power level. 